Coding apparatus, decoding apparatus, coding method and decoding method

ABSTRACT

There is disclosed an encoding device capable of improving similarity between the high frequency band spectrum of the original signal and a new spectrum to be generated while realizing a low bit rate when encoding a wide-band signal spectrum. The encoding device has sub-band amplitude calculation units for calculating the amplitude of the respective sub-bands for the high frequency band spectrum obtained from the wide-band signal. A search unit and a gain codebook select some sub-bands from a plurality of sub-bands and only the gain of the selected sub-bands is subjected to encoding. An interpolation unit expresses the gain of the sub-band not selected, by mutually interpolating the selected gains.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 11/596,254filed Nov. 13, 2006, which is a 371 application of PCT/JP2005/008963filed May 17, 2005, which is based on Japanese Application No.2004-148901 filed May 19, 2004, the entire contents of each of which areincorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a coding apparatus that codes thespectrum of a wideband voice signal, audio signal, or the like, adecoding apparatus, and a method thereof.

BACKGROUND ART

In the voice coding field, typical methods of coding a 50 Hz to 7 kHzwideband signal include the G722 and G722.1 standards of the ITU-T, andAMR-WB proposed by 3GPP (The 3rd Generation Partnership Project).According to these coding methods, it is possible to perform coding ofwideband voice signals with bit rates of 6.6 kbit/s to 64 kbit/s.However, the quality of such a signal, although high compared with anarrowband signal, is not adequate for audio signals or when morerealistic quality is required of a voice signal.

Generally, realism equivalent to FM radio can be obtained if the maximumfrequency of a signal is extended to around 10 to 15 kHz, and CD qualitycan be obtained if the maximum frequency is extended to around 20 kHz.An audio signal coding method such as the Layer 3 method standardized bythe MPEG (Moving Picture Expert Group) or the AAC (Advanced audiocoding) method is generally used for coding of such wideband signals.However, with these audio coding methods the bit rate of the codingparameter is high because the frequency band subject to coding is wide.

As a technology for performing high-quality coding of a wideband signalspectrum at a low bit rate, a technology is disclosed in Patent Document1 whereby the overall bit rate is reduced while suppressing qualitydegradation by replacing a high frequency band spectrum within awideband spectrum with a duplicate of a low frequency band spectrum, andthen performing envelope adjustment.

Also, in Patent Document 2 a technology is disclosed whereby the bitrate is reduced by dividing a spectrum into a plurality of subbands,calculating gain on a subband-by-subband basis and generating a gainvector, and performing vector quantization of this gain vector.

-   Patent Document 1: Japanese Patent Publication Laid-Open No.    2001-521648 (p. 15, FIG. 1, FIG. 2)-   Patent Document 2: Japanese Patent Application Laid-Open No. HEI    5-265487

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

FIGS. 1A through 1D are graphs showing spectra when the technologydisclosed in Patent Document 1 is applied to a 0≦k<FH frequency bandoriginal signal.

FIG. 1A shows the original signal spectrum, FIG. 1B the low frequencyband spectrum after elimination of the high frequency band (FL≦k<FH) ofthe original signal spectrum, FIG. 1C the spectrum of the entire bandobtained by inserting a duplicate of the low frequency band spectrum inFIG. 1B into the high frequency band, and FIG. 1D the spectrum afterenvelope adjustment of the high frequency band.

The reason for performing envelope adjustment after replacing the highfrequency band spectrum with a duplicate of the low frequency bandspectrum in this way is that it is known that major quality degradationwill occur if the outline of the newly generated high frequency bandspectrum (duplicate spectrum) differs greatly from the outline of thehigh frequency band spectrum of the original signal. Therefore,improving the similarity between the high frequency band spectrum of theoriginal signal and the newly generated spectrum by adjusting theoutline of the newly generated high frequency band spectrum is extremelyimportant.

A possible method of adjusting the outline of the high frequency bandspectrum is, for example, to multiply the duplicate spectrum by anadjustment coefficient (gain) so that the energy of the duplicatespectrum matches the energy of the high frequency band spectrum of theoriginal signal. FIGS. 2A and 2B are graphs showing an example of theoutline of a spectrum obtained by processing that multiplies thisduplicate spectrum by gain.

FIG. 2A shows the outline of the spectrum of the original signal, andFIG. 2B shows the outline of the spectrum after outline adjustment.

As can be seen from these figures, when the above-described spectrumoutline adjustment is performed, the following problem arises in theobtained spectrum. Namely, a discontinuity occurs at the juncture of thelow frequency band spectrum and high frequency band spectrum, causing andegraded sound. This is because, since the entire high frequency bandspectrum is multiplied uniformly by the same gain, the energy of thehigh frequency band spectrum matches that of the original signal, butcontinuity is not necessarily maintained between the low frequency bandspectrum and high frequency band spectrum. Also, if there is acharacteristic shape in the outline of the low frequency band spectrum,simply multiplying by the same uniform gain will result in thatcharacteristic shape remaining inappropriately, which will alsocontribute to degradation of sound quality.

Another possibility is, for example, application of the technology ofPatent Document 2 to the above-described spectrum outlineadjustment—that is, dividing the signal into subbands and thenperforming outline adjustment by adjusting gain on a subband-by-subbandbasis. FIGS. 3A and 3B are graphs showing an example of the outline of aspectrum obtained by this processing.

FIG. 3A shows the outline of the spectrum of the original signal, andFIG. 3B shows the outline of the spectrum when the signal has beendivided into subbands and the gain of each subband has been adjusted.

As can be seen from these figures, when the technology of PatentDocument 2 is applied, the shape of the high frequency band spectrum maybe inaccurate (it may not be possible to reproduce the shape of theoriginal signal). This happens because, in the method whereby gain isadjusted on a subband-by-subband basis, a sufficient number of bits arenot distributed when the number of subbands is increased and a largenumber of bits are fundamentally necessary in order to perform codingwith good precision. This situation may naturally occur since the wholepoint of replacing the high frequency band spectrum with a duplicate ofthe low frequency band spectrum is to achieve a lower bit rate.

As explained above, with a conventional method, when coding a widebandsignal spectrum it is difficult to improve the similarity between a highfrequency band spectrum of the original signal and a newly generatedspectrum while achieving a lowering of the bit rate.

Thus, it is an object of the present invention to provide a codingapparatus and coding method that enable the similarity between a highfrequency band spectrum of an original signal and a newly generatedspectrum to be improved while achieving a lowering of the bit rate whencoding a wideband signal spectrum.

Means for Solving the Problems

A coding apparatus of the present invention employs a configuration thatincludes: an acquisition section that acquires a spectrum divided intoat least a low frequency band and a high frequency band; a first codingsection that codes the tow frequency band spectrum; a second codingsection that codes the shape of the high frequency band spectrum; athird coding section that codes only gain of a specific location of thehigh frequency band spectrum; and an output section that outputs codedinformation obtained by the first, second, and third coding sections.

Advantageous Effect of the Invention

The present invention enables the similarity between a high frequencyband spectrum of an original signal and a newly generated spectrum to beimproved while achieving a lowering of the bit rate when coding awideband signal spectrum.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a graph showing the spectrum of an original signal;

FIG. 1B is a graph showing a low frequency band spectrum after a highfrequency band of the spectrum of the original signal has beeneliminated;

FIG. 1C is a graph showing the spectrum of the entire band obtained byinserting a duplicate of the low frequency band spectrum into the highfrequency band;

FIG. 1D is a graph showing the spectrum after envelope adjustment of thehigh frequency band;

FIG. 2A is a graph showing the outline of the spectrum of an originalsignal;

FIG. 2B is a graph showing the outline of the spectrum after outlineadjustment;

FIG. 3A is a graph showing the outline of the spectrum of an originalsignal;

FIG. 3B is a graph showing the outline of the spectrum when the signalhas been divided into subbands and the gain of each subband has beenadjusted;

FIG. 4 is a block diagram showing the main configuration elements of aradio transmitting apparatus according to Embodiment 1;

FIG. 5 is a block diagram showing the main internal configurationelements of a coding apparatus according to Embodiment 1;

FIG. 6 is a block diagram showing the main internal configurationelements of a high frequency band coding section according to Embodiment1;

FIG. 7 is a block diagram showing the main internal configurationelements of a gain coding section according to Embodiment 1;

FIG. 8A is a graph for explaining a series of processes relating tointerpolation computation according to Embodiment 1;

FIG. 8B is a graph for explaining a series of processes relating tointerpolation computation according to Embodiment 1;

FIG. 9 is a graph showing a case in which there is only one quantizationpoint, g1(j);

FIG. 10A is a graph showing a case in which there are three quantizationpoints;

FIG. 10B is a graph showing a case in which there are three quantizationpoints;

FIG. 11 is a block diagram showing another variation of a codingapparatus according to Embodiment 1;

FIG. 12 is a block diagram showing the main configuration elements of ahigh frequency band coding section according to Embodiment 1;

FIG. 13 is a block diagram showing the main configuration elements of aradio receiving apparatus according to Embodiment 1;

FIG. 14 is a block diagram showing the main internal configurationelements of a decoding apparatus according to Embodiment 1;

FIG. 15 is a block diagram showing the main internal configurationelements of a high frequency band decoding section according toEmbodiment 1;

FIG. 16 is a drawing showing the configuration of a decoding apparatusaccording to Embodiment 1;

FIG. 17 is a block diagram showing the main configuration elements of ahigh frequency band decoding section according to Embodiment 1;

FIG. 18A is a block diagram showing the main configuration elements onthe transmitting side when a coding apparatus according to Embodiment 1is applied to a cable communication system;

FIG. 18B is a block diagram showing the main configuration elements onthe receiving side when a decoding apparatus according to Embodiment 1is applied to a cable communication system;

FIG. 19 is a block diagram showing the main configuration elements of alayered coding apparatus according to Embodiment 2;

FIG. 20 is a block diagram showing the main internal configurationelements of a spectrum coding section according to Embodiment 2;

FIG. 21 is a block diagram showing the main internal configurationelements of an extension band gain coding section according toEmbodiment 2;

FIG. 22A is a graph for explaining in outline the processing of anextension band gain coding section according to Embodiment 2;

FIG. 22B is a graph for explaining in outline the processing of anextension band gain coding section according to Embodiment 2;

FIG. 23 is a block diagram showing the internal configuration of alayered decoding apparatus according to Embodiment 2;

FIG. 24 is a block diagram showing the internal configuration of aspectrum decoding apparatus according to Embodiment 2;

FIG. 25 is a block diagram showing the main internal configurationelements of an extension band gain decoding section according toEmbodiment 2;

FIG. 26 is a block diagram showing the main internal configurationelements of an extension band gain coding section according toEmbodiment 3;

FIG. 27 is a graph for explaining the base amplitude value calculationmethod;

FIG. 28 is a graph for explaining interpolation processing of aninterpolation section according to Embodiment 3;

FIG. 29 is a drawing explaining the configuration of a decodingapparatus according to Embodiment 3;

FIG. 30 is a block diagram showing the main configuration elements of anextension band gain coding section according to Embodiment 4;

FIG. 31 is a graph for explaining the gain candidate allocation methodof an interpolation section according to Embodiment 4; and

FIG. 32 is a drawing explaining an extension band gain decoding sectionaccording to Embodiment 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings. Here, cases in which anaudio signal or voice signal is coded/decoded will be described as anexample. Two cases can broadly be considered for the present invention:a first case in which it is applied to normal coding (non-scalablecoding), and a second case in which it is applied to scalable coding.The first case will be described in Embodiment 1, and the second case inEmbodiment 2.

Embodiment 1

FIG. 4 is a block diagram showing the main configuration elements of aradio transmitting apparatus 130 when a coding apparatus according toEmbodiment 1 of the present invention is provided on the transmittingside of a radio communication system.

This radio transmitting apparatus 130 has a coding apparatus 100, aninput apparatus 131, an A/D conversion apparatus 132, an RF modulationapparatus 133, and an antenna 134.

Input apparatus 131 converts a sound wave W11 audible to the human earto an analog signal that is an electrical signal, and outputs thissignal to A/D conversion apparatus 132. A/D conversion apparatus 132converts this analog signal to a digital signal, and outputs this signalto coding apparatus 100. Coding apparatus 100 codes the input digitalsignal and generates a coded signal, and outputs this signal to RFmodulation apparatus 133. RF modulation apparatus 133 modulates thecoded signal and generates a modulated coded signal, and outputs thissignal to antenna 134. Antenna 134 transmits the modulated coded signalas a radio wave W12.

FIG. 5 is a block diagram showing the main internal configurationelements of above-described coding apparatus 100. As an example, a casewill here be described in which a time-domain digital signal is input,and this signal is converted to a frequency-domain signal before beingcoded.

Coding apparatus 100 has an input terminal 101, a frequency-domainconversion section 102, a division section 103, a low frequency bandcoding section 104, a high frequency band coding section 105, amultiplexing section 106, and an output terminal 107.

Frequency-domain conversion section 102 converts a time-domain digitalsignal input from input terminal 101 to the frequency domain, andgenerates a spectrum comprising a frequency-domain signal. The validfrequency band of this spectrum is assumed to be 0≦k<FH. Methods forperforming conversion to the frequency domain include discrete Fouriertransform, discrete cosine transform, modified discrete cosinetransform, wavelet transform, and so forth.

Division section 103 divides the spectrum obtained by frequency-domainconversion section 102 into two frequency bands comprising a lowfrequency band spectrum and high frequency band spectrum, and sends thedivided spectra to low frequency band coding section 104 and highfrequency band coding section 105. Specifically, division section 103divides the spectrum output from frequency-domain conversion section 102into a low frequency band spectrum with a 0≦k<FL valid frequency band,and a high frequency band spectrum with an FL≦k<FH valid frequency band,and sends the obtained low frequency band spectrum to low frequency bandcoding section 104, and the high frequency band spectrum to highfrequency band coding section 105.

Low frequency band coding section 104 performs coding of the lowfrequency band spectrum output from division section 103, and outputsthe obtained coded information to multiplexing section 106. In the caseof audio data or voice data, low frequency band data is more importantthan high frequency band data, and therefore more bits are distributedto low frequency band coding section 104, and higher-quality codingperformed, than for high frequency band coding section 105. A methodsuch as the MPEG Layer 3 method, AAC method, TwinVQ (Transform domainWeighted INterleave Vector Quantization) method, or the like is used asthe actual coding method.

High frequency band coding section 105 performs coding processingdescribed later herein on the high frequency band spectrum output fromdivision section 103, and outputs the obtained coded information (gaininformation) to multiplexing section 106. A detailed description of thecoding method used in high frequency band coding section 105 will begiven later herein.

In multiplexing section 106, information relating to the low frequencyband spectrum is input from low frequency band coding section 104, whilegain information necessary for obtaining the outline of the highfrequency band spectrum is input from high frequency band coding section105. Multiplexing section 106 multiplexes these items of information andoutputs them from output terminal 107.

FIG. 6 is a block diagram showing the main internal configurationelements of above-described high frequency band coding section 105.

A spectrum shape coding section 112 receives input signal spectrum S(k)with an FL≦k<FH valid frequency via an input terminal 111, and performscoding of the shape of this spectrum. Specifically, spectrum shapecoding section 112 codes the spectrum shape so that auditory distortionbecomes minimal, and sends coded information relating to this spectrumshape to a multiplexing section 114 and a spectrum shape decodingsection 116.

As the spectrum shape coding method, for example, code vector C(i,k)when square distortion E expressed by Equation (1) is minimal is found,and this code vector C(i,k) is output.

$\begin{matrix}{E = {\sum\limits_{k = {FL}}^{{FH} - 1}\;{{w(k)} \cdot \left( {{S(k)} - {C\left( {i,k} \right)}} \right)^{2}}}} & {{Equation}\mspace{14mu}(1)}\end{matrix}$

Here, C(i,k) represents the i'th code vector contained in the codebook,and w(k) represents a weighting factor corresponding to the auditoryimportance of frequency k. FL and FH represent indices corresponding tothe minimum frequency and maximum frequency respectively of the highfrequency band spectrum. Spectrum shape coding section 112 may alsooutput a code vector C(i,k) that minimizes Equation (2).

$\begin{matrix}{E = {{\sum\limits_{k = {FL}}^{{FH} - 1}\;{S(k)}^{2}} - \frac{\left( {\sum\limits_{k = {FL}}^{{FH} - 1}\;{{S(k)} \cdot {C\left( {i,k} \right)}}} \right)^{2}}{\sum\limits_{k = {FL}}^{{FH} - 1}\;{C\left( {i,k} \right)}^{2}}}} & {{Equation}\mspace{14mu}(2)}\end{matrix}$

As the first term on the right side of this equation is a constant term,a code vector that maximizes the second term on the right side may alsobe thought of as being output.

Spectrum shape decoding section 116 decodes coded information relatingto the spectrum shape output from spectrum shape coding section 112, andsends obtained code vector C(i,k) to a gain coding section 113.

Gain coding section 113 codes the gain of code vector C(i,k) so that theoutline of the spectrum of code vector C(i,k) approaches the outline ofinput spectrum S(k), the target signal, and sends coded information tomultiplexing section 114. Gain coding section 113 processing will bedescribed in detail later herein.

Multiplexing section 114 multiplexes the coded information output fromspectrum shape coding section 112 and gain coding section 113, andoutputs this information via an output terminal 115.

FIG. 7 is a block diagram showing the main internal configurationelements of above-described gain coding section 113. The shape of thehigh frequency band spectrum is input to gain coding section 113 fromspectrum shape decoding section 116 via an input terminal 121, and theinput spectrum is input via an input terminal 127.

A subband amplitude calculation section 122 calculates the amplitudevalue of each subband for the spectrum shape input from spectrum shapedecoding section 116. A multiplication section 123 multiplies theamplitude value of each subband of the spectrum shape output fromsubband amplitude calculation section 122 by the gain of each subband(described later herein) output from an interpolation section 126 andadjusts the amplitude, and then outputs the result to a search section124. Meanwhile, a subband amplitude calculation section 128 calculatesthe amplitude value of each subband for the input spectrum of the targetsignal input from input terminal 127, and outputs the result to searchsection 124.

Search section 124 calculates distortion between subband amplitudevalues output from multiplication section 123 and high frequency bandspectrum subband amplitude values sent from subband amplitudecalculation section 128. Specifically, a plurality of gain quantizationvalue candidates g(j) are recorded beforehand in a gain codebook 125,and search section 124 specifies one of these gain quantization valuecandidates g(j), and calculates the above-described distortion (squaredistortion) for this candidate. Here, j is an index for identifying eachgain quantization value candidate. Gain codebook 125 sends the gaincandidate g(j) specified by search section 124 to interpolation section126. Using this gain candidate g(j), interpolation section 126calculates the gain value of a subband for which gain has not yet beendetermined, by means of an interpolation computation. Then interpolationsection 126 sends the gain candidate provided by gain codebook 125 andthe calculated interpolated gain candidate to multiplication section123.

The processing of above-described multiplication section 123, searchsection 124, gain codebook 125, and interpolation section 126 forms afeedback loop, and search section 124 calculates the above-describeddistortion (square distortion) for all gain quantization valuecandidates g(j) recorded in gain codebook 125. Then search section 124outputs index j of the gain for which square distortion is smallest viaan output terminal 129. To describe the above processing in other words,search section 124 first selects a specific value from among gainquantization value candidates g(j) recorded in gain codebook 125, andgenerates a dummy high frequency band spectrum by interpolating theremaining gain quantization values using this value. Then this generatedspectrum and the high frequency band spectrum of the target signal arecompared and the similarity of the two spectra is determined, and searchsection 124 finally selects not the gain quantization value candidateused initially but the gain quantization value for which the similaritybetween the two spectra is the best, and outputs index j indicating thisgain quantization value.

FIGS. 8A and 8B are graphs for explaining the above-described series ofprocesses relating to interpolation computation in gain coding section113. Here, as an example, a case will be described, in which the numberof subbands N of the high frequency band spectrum is 8. Gain codebook125 has gain candidates G(j)={g0(j), g1(j)}, having 0'th subband gaincandidate g0(j) and 7th subband gain candidate g1(j) as elements. Here,j represents an index for identifying the gain candidate. Gain codebook125 is designed beforehand using learning data of sufficient length, andtherefore has suitable gain candidates stored in it.

Gain candidates G(j) may be scalar values or vector values, but willhere be described as 2-dimensional vector values. Using gain candidatesG(j), interpolation section 126 calculates gain for subbands whose gainhas not yet been determined, by means of interpolation.

Specifically, interpolation processing is performed as shown in FIG. 8B.The 0'th subband gain is given by g0(j), and the 7th subband gain byg1(j), and the gain values of the other subbands are given asinterpolated values by linear interpolation of g0(j) and g1(j).

Thus, according to a coding apparatus of this embodiment, an inputwideband spectrum to be coded is divided into at least a low frequencyband spectrum and a high frequency band spectrum, the high frequencyband spectrum is further divided into a plurality of subbands, somesubbands are selected from this plurality of subbands, and only the gainof the selected subbands is made subject to coding (quantization). Thus,since coding is not performed for all the subbands, gain can be codedefficiently with a small number of bits. The reason for executing theabove-described processing on the high frequency band spectrum is that,when the input signal is an audio signal, voice signal, or the like,high frequency band data is of less importance than low frequency banddata.

In the above configuration, a coding apparatus according to thisembodiment represents the gains of non-selected subbands in the highfrequency band spectrum by reciprocal interpolation of the selectedgains. Thus, gain can be determined while smoothly approximatingvariations in the spectrum outline, with the number of bits maintainedat a certain level. That is to say, the occurrence of degraded soundscan be suppressed, and quality is improved, with a small number of bits.Thus, when coding the spectrum of a wideband signal, the similaritybetween a high frequency band spectrum of the original signal and anewly generated spectrum can be improved while achieving a lowering ofthe bit rate.

The present invention focuses on the fact that the outline of a spectrumvaries smoothly in the frequency axis direction, and making use of thisproperty, limits points subject to coding (quantization points) to somethereof, codes only these quantization points, and finds thequantization point gain for other subbands by reciprocal interpolation.

In the above configuration, a transmitting apparatus equipped with acoding apparatus according to this embodiment transmits only thequantized gain of a selected subband, and does not transmit gainobtained by interpolation. On the other hand, a decoding apparatusprovided in the receiving apparatus receives and decodes transmittedquantized gain, and reciprocally interpolates transmitted gain fornon-transmitted subband gain. Use of these configurations lowers thetransmission rate between transmitting and receiving apparatuses,enabling the communication system load to be reduced.

In this embodiment, a case in which linear interpolation of gain isperformed has been described as an example, but the interpolation methodis not limited to this, and if, for example, it is known that codingperformance will be improved more by performing interpolation with afunction other than a linear function, that function may be used forinterpolation computations.

In this embodiment, a case in which the gains of subbands at theabove-described locations are selected as quantization points—that is acase in which g0(j) is the gain of the subband with the lowest frequencyof the high frequency band spectrum, and g1(j) is the gain of thesubband with the highest frequency of the high frequency bandspectrum—has been described as an example. While the locations of thequantization points are not necessarily limited to these settings, errordue to interpolation can be expected to be reduced by meeting thefollowing conditions. In particular, in order to maintain continuitybetween the low frequency band spectrum and high frequency bandspectrum, it is desirable for the location of g0(j) to be set close tofrequency FL, the juncture between the low frequency band spectrum andhigh frequency band spectrum. However, even if the location of g0(j) isset in this way, the low frequency band spectrum and the (newlygenerated) high frequency band spectrum will not necessarily beconnected smoothly. Nevertheless, there will probably not be a majordegradation of sound quality as long as continuity is at leastmaintained. Also, by setting g1(j) at the location of the subband withthe highest frequency of the high frequency band spectrum (in short, atthe right end of the high frequency band spectrum), as long as the gainof this location at least can be specified, generally speaking it willprobably be possible to represent the outline of the entire highfrequency band spectrum efficiently, although perhaps with roughprecision. However, the location of g1(j) may also be intermediatebetween FL and FH, for example.

In this embodiment, a case in which there are two quantization points,g0(j) and g1(j), has been described as an example, but there may also bea single quantization point. This case will be described in detailbelow, using the accompanying drawings.

FIG. 9 is a graph showing a case in which there is only one quantizationpoint, g1(j). In this figure, SL indicates the low frequency bandspectrum and SH indicates the high frequency band spectrum. As the gainvalue of the highest-frequency subband of the low frequency bandspectrum can be expected not to differ greatly from the gain value ofthe lowest-frequency subband of the high frequency band spectrum in thisway, the gain value of the highest-frequency subband of the lowfrequency band spectrum is used instead of g0(j). This makes it possibleto perform the above-described interpolation without finding g0(j).

Three or more quantization points may also be used. FIGS. 10A and 10Bare graphs showing a case in which there are three quantization points.

As shown in these figures, subband gains determined in three subbandsare used, and the gains of other subbands are determined byinterpolation. By using three or more quantization points in this way,even if two points are used to represent gain at the ends of the highfrequency band spectrum (FL and FH), at least one point can be locatedin the middle of the high frequency band spectrum (the part other thanthe ends). Therefore, even if there is a distinctive part in the outlineof the high frequency band spectrum, such as a peak (maximum point) or adip (minimum point), by assigning one quantization point to this peak ordip it is possible to generate coding parameters that represent the highfrequency band spectrum outline with good precision. However, althoughsmall variations in the spectrum outline can be coded more faithfully ifthe number of quantization points is increased to three or more, codingefficiency falls as a trade-off.

In this embodiment, a case has been described by way of example in whichthe coding method comprises a step of selecting some quantization pointsfrom a plurality of subbands, and a step of obtaining the remaining gainvalues by means of interpolation computations, but since a lower bitrate can be achieved simply by limiting quantization points to afraction of the total, if high coding performance is not required theinterpolation computation step may be omitted, and only the step ofselecting some quantization points performed.

In this embodiment, a case in which subbands are generated by dividingthe band at equal intervals has been described as an example, but thisis not a limitation, and a nonlinear division method using a Bark scale,for example, may also be used.

In this embodiment, a case in which an input digital signal is converteddirectly to the frequency domain before performing band division hasbeen described as an example, but this is not a limitation.

FIG. 11 is a block diagram showing another variation of above-describedcoding apparatus 100 (coding apparatus 100 a). Identical configurationelements are assigned the same codes.

As shown in this figure, a configuration may also be employed wherebyband division is performed by executing filter processing on an inputdigital signal. In this case, band division is performed using apolyphase filter, quadrature mirror filter, or the like.

FIG. 12 is a block diagram showing the main configuration elements of ahigh frequency band coding section 105 a in coding apparatus 100 a.Configuration elements identical to those in high frequency band codingsection 105 are assigned the same codes. The difference between highfrequency band coding section 105 and high frequency band coding section105 a is the location of the frequency-domain conversion section.

The coding-side configuration has been described in detail above. Next,the decoding-side configuration will be described in detail.

FIG. 13 is a block diagram showing the main configuration elements of aradio receiving apparatus 180 that receives a signal transmitted fromradio transmitting apparatus 130 according to this embodiment.

Radio receiving apparatus 180 has an antenna 181, an RF demodulationapparatus 182, a decoding apparatus 150, a D/A conversion apparatus 183,and an output apparatus 184.

Antenna 181 receives a digital coded sound signal as radio wave W12 andgenerates an electrical signal that is a digital received coded soundsignal, and sends this signal to RF demodulation apparatus 182. RFdemodulation apparatus 182 demodulates the received coded sound signalfrom antenna 181 and generates a demodulated coded sound signal, andsends this signal to decoding apparatus 150.

Decoding apparatus 150 receives the digital demodulated coded soundsignal from RF demodulation apparatus 182, performs decoding processingand generates a digital decoded sound signal, and sends this signal toD/A conversion apparatus 183. D/A conversion apparatus 183 converts thedigital decoded voice signal from decoding apparatus 150 and generatesan analog decoded voice signal, and sends this signal to outputapparatus 184. Output apparatus 184 converts the electrical analogdecoded voice signal to air vibrations and outputs these vibrations as asound wave W13 audible to the human ear.

FIG. 14 is a block diagram showing the main internal configurationelements of above-described decoding apparatus 150.

A separation section 152 separates low frequency band coding parametersand high frequency band coding parameters from a demodulated decodedsound signal input via an input terminal 151, and sends these codingparameters to a low frequency band decoding section 153 and a highfrequency band decoding section 154 respectively. Low frequency banddecoding section 153 decodes the coding parameters obtained by codingprocessing of low frequency band coding section 104 and generates a lowfrequency band decoded spectrum, and sends this to a combining section155. High frequency band decoding section 154 performs decodingprocessing using the high frequency band coding parameters, generates ahigh frequency band decoded spectrum, and sends this to combiningsection 155. Details of high frequency band decoding section 154 will begiven later herein. Combining section 155 combines the low frequencyband decoded spectrum and high frequency band decoded spectrum, andsends the combined spectrum to a time-domain conversion section 156.Time-domain conversion section 156 converts the combined spectrum to thetime domain, and also performs processing such as windowing andoverlapped addition to deter the occurrence of discontinuities betweenconsecutive frames, and outputs the result from an output terminal 157.

FIG. 15 is a block diagram showing the main internal configurationelements of high frequency band decoding section 154.

A separation section 162 separates a spectrum shape code and gain codefrom high frequency band coding parameters input via an input terminal161, and sends these to a spectrum shape decoding section 163 and a gaindecoding section 164 respectively. Spectrum shape decoding section 163references the spectrum shape code and selects code vector C(i,k) fromthe codebook, and sends this to a multiplication section 165. Gaindecoding section 164 decodes gain based on the gain code, and sends thisto multiplication section 165. Details of this gain decoding section 164will be given in Embodiment 2. Multiplication section 165 multiplies thecode vector C(i,k) selected by spectrum shape decoding section 163 bythe gain decoded by gain decoding section 164, and outputs the resultvia an output terminal 166.

When the coding-side configuration is such as to perform band divisioninto a low frequency band signal and high frequency band signal by meansof a band division filter, as in the case of coding apparatus 100 ashown in FIG. 11, the configuration of a corresponding decodingapparatus is as shown in FIG. 16 (decoding apparatus 150 a). Identicalconfiguration elements are assigned the same codes. FIG. 17 is a blockdiagram showing the main configuration elements of a high frequency banddecoding section 154 a in decoding apparatus 150 a. The differencebetween high frequency band decoding section 154 and high frequency banddecoding section 154 a is the location of the time-domain conversionsection.

Thus, according to the above-described decoding apparatus, informationcoded by a coding apparatus according to this embodiment can be decoded.

In this embodiment, a case in which the frequency band of an inputsignal is divided into two bands has been described as an example, butthis is not a limitation, and it is possible to perform division intotwo or more bands and perform the previously described spectrum codingprocessing on one or a plurality thereof.

In this embodiment, a case in which a time-domain signal is input hasbeen described as an example, but a frequency-domain signal may also beinput directly.

A case in which a coding apparatus or decoding apparatus according tothis embodiment is applied to a radio communication system has beendescribed here as an example, but a coding apparatus or decodingapparatus according to this embodiment can also be applied to a cablecommunication system as described below.

FIG. 18A is a block diagram showing the main configuration elements onthe transmitting side when a coding apparatus according to thisembodiment is applied to a cable communication system. Configurationelements identical to those already shown in FIG. 4 are assigned thesame codes as in FIG. 4, and descriptions thereof are omitted.

A cable transmitting apparatus 140 has a coding apparatus 100, inputapparatus 131, and A/D conversion apparatus 132, and its output isconnected to a network N1.

The input terminal of A/D conversion apparatus 132 is connected to theoutput terminal of input apparatus 131. The input terminal of codingapparatus 100 is connected to the output terminal of A/D conversionapparatus 132. The output terminal of coding apparatus 100 is connectedto network N1.

Input apparatus 131 converts sound wave W11 audible to the human ear toan analog signal that is an electrical signal, and sends this signal toA/D conversion apparatus 132. A/D conversion apparatus 132 converts thisanalog signal to a digital signal, and sends this signal to codingapparatus 100. Coding apparatus 100 codes the input digital signal andgenerates code, and outputs this to network N1.

FIG. 18B is a block diagram showing the main configuration elements onthe receiving side when a decoding apparatus according to thisembodiment is applied to a cable communication system. Configurationelements identical to those already shown in FIG. 13 are assigned thesame codes as in FIG. 13, and descriptions thereof are omitted.

A cable receiving apparatus 190 has a receiving apparatus 191 connectedto network N1, and a decoding apparatus 150, D/A conversion apparatus183, and output apparatus 184.

The input terminal of receiving apparatus 191 is connected to networkN1. The input terminal of decoding apparatus 150 is connected to theoutput terminal of receiving apparatus 191. The input terminal of D/Aconversion apparatus 183 is connected to the output terminal of decodingapparatus 150. The input terminal of output apparatus 184 is connectedto the output terminal of D/A conversion apparatus 183.

Receiving apparatus 191 receives a digital coded sound signal fromnetwork N1 and generates a digital received sound signal, and sends thissignal to decoding apparatus 150. Decoding apparatus 150 receives thereceived sound signal from receiving apparatus 191, performs decodingprocessing on this received sound signal and generates a digital decodedsound signal, and sends this signal to D/A conversion apparatus 183. D/Aconversion apparatus 183 converts the digital decoded voice signal fromdecoding apparatus 150 and generates an analog decoded voice signal, andsends this signal to output apparatus 184. Output apparatus 184 convertsthe electrical analog decoded sound signal to air vibrations and outputsthese vibrations as sound wave W13 audible to the human ear.

Thus, according to the above-described configurations, cabletransmitting and receiving apparatuses can be provided that have thesame kind of operational effects as the above-described radiotransmitting and receiving apparatuses.

Embodiment 2

A characteristic of this embodiment is that a coding apparatus anddecoding apparatus of the present invention are applied to scalable bandcoding having scalability in the frequency axis direction.

FIG. 19 is a block diagram showing the main configuration elements of alayered coding apparatus 200 according to Embodiment 2 of the presentinvention.

Layered coding apparatus 200 has an input terminal 221, a down-samplingsection 222, a first layer coding section 223, a first layer decodingsection 224, a delay section 226, a spectrum coding section 210, amultiplexing section 227, and an output terminal 228.

A signal with a 0≦k<FH valid frequency band is input to input terminal221 from A/D conversion apparatus 132. Down-sampling section 222executes down-sampling on the signal input via input terminal 221, andgenerates and outputs a low-sampling-rate signal. First layer codingsection 223 codes the down-sampled signal and outputs the obtainedcoding parameter to multiplexing section (multiplexer) 227 and also tofirst layer decoding section 224. First layer decoding section 224generates a first layer decoded signal based on this coding parameter.

Meanwhile, delay section 226 imparts a delay of predetermined length tothe signal input via input terminal 221. The length of this delay isequal to the time lag when first layer coding section 223 and firstlayer decoding section 224 are passed through. Spectrum coding section210 performs spectrum coding with the signal output from first layerdecoding section 224 as a first signal and the signal output from delaysection 226 as a second signal, and outputs the generated codingparameter to multiplexing section 227. Multiplexing section 227multiplexes the coding parameter obtained by first layer coding section223 and the coding parameter obtained by spectrum coding section 210,and outputs the result as output code via output terminal 228. Thisoutput code is sent to RF modulation apparatus 133.

FIG. 20 is a block diagram showing the main internal configurationelements of above-described spectrum coding section 210.

Spectrum coding section 210 has input terminals 201 and 204,frequency-domain conversion sections 202 and 205, an extension bandspectrum estimation section 203, an extension band gain coding section206, a multiplexing section 207, and an output terminal 208.

The signal decoded by first layer decoding section 224 is input to inputterminal 201. The valid frequency band of this signal is 0≦k<FL. Thesecond signal with an valid frequency band of 0≦k<FH (where FL<FH) isinput to input terminal 204 from delay section 226.

Frequency-domain conversion section 202 performs frequency conversion onthe first signal input from input terminal 201, and calculates a firstspectrum S1(k). Frequency-domain conversion section 205 performsfrequency conversion on the second signal input from input terminal 204,and calculates a second spectrum S2(k). The frequency conversion methodused here is discrete Fourier transform (DFT), discrete cosine transform(DCT), modified discrete cosine transform (MDCT), or the like.

Extension band spectrum estimation section 203 estimates the spectrumthat should be included in band FL≦k<FH of first spectrum S1(k) withsecond spectrum S2(k) as a reference signal, and finds estimatedspectrum E(k) (where FL≦k<FH). Here, estimated spectrum E(k) isestimated based on a spectrum included in the low frequency band(0≦k<FL) of first spectrum S1(k).

Extension band gain coding section 206 codes the gain by which estimatedspectrum E(k) should be multiplied using estimated spectrum E(k) andsecond spectrum S2(k). In the processing here, it is particularlyimportant that the spectrum outline of estimated spectrum E(k) in theextension band be made to approximate the spectrum outline of secondspectrum S2(k) efficiently and with a small number of bits. Whether ornot this is achieved greatly affects the sound quality.

Information relating to the estimated spectrum of the extension band isinput to multiplexing section 207 from extension band spectrumestimation section 203, and gain information necessary for obtaining thespectrum outline of the extension band is input to multiplexing section207 from extension band gain coding section 206. These items ofinformation are multiplexed and then output from output terminal 208.

FIG. 21 is a block diagram showing the main internal configurationelements of above-described extension band gain coding section 206.

This extension band gain coding section 206 has input terminals 211 and217, subband amplitude calculation sections 212 and 218, a gain codebook215, an interpolation section 216, a multiplication section 213, asearch section 214, and an output terminal 219.

Estimated spectrum E(k) is input from input terminal 211, and secondspectrum S2(k) is input from input terminal 217. Subband amplitudecalculation section 212 divides the extension band into subbands, andcalculates the amplitude value of estimated spectrum E(k) for eachsubband. When the extension band is expressed as FL≦k<FH, bandwidth BWof the extension band is expressed by Equation (3).BW=FH−FL+1  Equation (3)

When this extension band is divided into N subbands, bandwidth BW ofeach subband is expressed by Equation (4).BWS=(FH−FL+1)/N  Equation (4)

Thus, minimum frequency FL(n) of the nth subband is expressed byEquation (5), and maximum frequency FH(n) is expressed by Equation (6).FL(n)=FL+n·BWS  Equation (5)FH(n)=FL+(n+1)·BWS−1  Equation (6)

Amplitude value AE(n) of estimated spectrum E(k) stipulated in this wayis calculated in accordance with Equation (7).

$\begin{matrix}{{{AE}(n)} = \sqrt{\frac{\sum\limits_{k = {{FL}{(n)}}}^{{FH}{(n)}}\;{E(k)}^{2}}{BWS}}} & {{Equation}\mspace{14mu}(7)}\end{matrix}$

Similarly, subband amplitude calculation section 218 calculatesamplitude value AS2(n) of each subband of second spectrum S2(k) inaccordance with Equation (8).

$\begin{matrix}{{{AS}\; 2(n)} = \sqrt{\frac{\sum\limits_{k = {{FL}{(n)}}}^{{FH}{(n)}}\;{S\; 2(k)^{2}}}{BWS}}} & {{Equation}\mspace{14mu}(8)}\end{matrix}$

Meanwhile, gain codebook 215 has J gain quantization value candidatesG(j) (where 0≦j<J), and executes the following processing for all gaincandidates. Gain candidates G(j) may be scalar values or vector values,but for purposes of explanation will here be assumed to be 2-dimensionalvector values (that is, g(j)={g0(j), g1(j)}). Gain codebook 215 isdesigned beforehand using learning data of sufficient length, andtherefore has suitable gain candidates stored in it.

FIGS. 22A and 22B are graphs for explaining in outline the processing ofextension band gain coding section 206. Here, also, a case will bedescribed by way of example in which number of subbands N=8.

As shown in FIG. 22A, first element g0(j) of gain candidates G(j) istaken as the 0'th subband gain, and second element g1(j) as the 7thsubband gain, and these are allocated to the 1st subband and 7thsubband.

Using these gain candidates G(j), interpolation section 216 calculatesgain for subbands whose gain has not yet been determined, by means ofinterpolation.

Specifically, this is performed as shown in FIG. 22B. The 0'th subbandgain is given by g0(j), and the 7th subband gain by g1(j), and the gainvalues of the other subbands are given as interpolated values of g0(j)and g1(j). Based on this concept, gain p(j,n) of the nth subband can beexpressed as shown in Equation (9).

$\begin{matrix}{{p\left( {j,n} \right)} = {{g\; 0(j)} + {\frac{{g\; 1(j)} - {g\; 0(j)}}{N - 1} \cdot {n\left( {0 \leq n \leq {N - 1}} \right)}}}} & {{Equation}\mspace{14mu}(9)}\end{matrix}$

Subband, gain candidate p(j,n) calculated in this way is sent tomultiplication section 213. Multiplication section 213 multipliestogether subband amplitude value AE(n) from subband amplitudecalculation section 212 and subband gain candidate p(j,n) frominterpolation section 216 for each element. If the post-multiplicationsubband amplitude value is expressed as AE′(n), AE′(n) is calculated inaccordance with Equation (10), and is sent to search section 214.AE′(n)=AE(n)·p(j,n)  Equation (10)

Search section 214 calculates distortion between post-multiplicationsubband amplitude value AE′(n) and second spectrum subband amplitudevalue AS2(k) sent from subband amplitude calculation section 218. Here,to simplify the explanation, a case in which square distortion is usedhas been described as an example, but, for example, a distance scalewhereby weighting is performed based on auditory sensitivity for eachelement or the like can also be used as a distortion definition.

Search section 214 calculates square distortion D between AE′(n) andAS2(n) in accordance with Equation (11).

$\begin{matrix}{D = {\sum\limits_{n = 0}^{N - 1}\;\left( {{{AS}\; 2(n)} - {{AE}^{\prime}(n)}} \right)^{2}}} & {{Equation}\mspace{14mu}(11)}\end{matrix}$

Square distortion D may also be expressed as shown in Equation (12).

$\begin{matrix}{D = {\sum\limits_{n = 0}^{N - 1}\;{{w(n)} \cdot \left( {{{AS}\; 2(n)} - {{AE}^{\prime}(n)}} \right)^{2}}}} & {{Equation}\mspace{14mu}(12)}\end{matrix}$

In this case, w(n) indicates a weighting function based on auditorysensitivity.

Square distortion D is calculated by means of the above-describedprocessing for all gain quantization value candidates G(j) included ingain codebook 215, and index j of the gain when square distortion D issmallest is output via output terminal 219.

Based on such processing, gain can be determined while smoothlyapproximating variations in the spectrum outline, enabling theoccurrence of degraded sounds to be suppressed and quality to beimproved with a small number of bits.

In this embodiment, gain is determined by performing interpolation basedon the amount of subband amplitude, but a configuration may also be usedwhereby interpolation is performed based on subband logarithmic energyinstead of subband amplitude. In this case, gain is determined so thatthe spectrum outline changes smoothly in a domain of logarithmic energyappropriate to human hearing characteristics, with the result thatauditory quality is further improved.

FIG. 23 is a block diagram showing the internal configuration of alayered decoding apparatus 250 that decodes information coded byabove-described layered coding apparatus 200. Here, a case in whichlayered-coded coding parameters are decoded will be described as anexample.

This layered decoding apparatus 250 has an input terminal 171, aseparation section 172, a first layer decoding section 173, a spectrumdecoding section 260, and output terminals 176 and 177.

A digital demodulated coded sound signal is input to input terminal 171from RF demodulation apparatus 182. Separation section 172 splits thedemodulated coded sound signal input via input terminal 171, andgenerates, a coding parameter for first layer decoding section 173 and acoding parameter for spectrum decoding section 260. First layer decodingsection 173 decodes a decoded signal with a 0≦k<FL signal band using acoding parameter obtained by separation section 172, and sends thisdecoded signal to the spectrum decoding section. The other output isconnected to output terminal 176. By this means, when it is necessary tooutput a first layer decoded signal generated by first layer decodingsection 173, it can be output via this output terminal 176.

The coding parameter separated by separation section 172 and first layerdecoded signal obtained by the first layer decoding section are sent tospectrum decoding section 260. Spectrum decoding section 260 performsspectrum decoding described later herein, generates a 0≦k<FH signal banddecoded signal, and outputs this signal via output terminal 177.Spectrum decoding section 260 performs processing regarding the firstlayer decoded signal sent from the first layer decoding section as afirst signal.

According to this configuration, when it is necessary to output a firstlayer decoded signal generated by first layer decoding section 173, itcan be output from output terminal 176. Also, if it is necessary tooutput a higher-quality spectrum decoding section 260 output signal,this signal can be output from output terminal 177. An output terminal176 or output terminal 177 signal is output from layered decodingapparatus 250, and is input to D/A conversion apparatus 183. Whichsignal is output is based on an application, user setting, ordetermination result.

FIG. 24 is a block diagram showing the internal configuration ofabove-described spectrum decoding section 260.

Spectrum decoding section 260 has input terminals 251 and 253, aseparation section 252, a frequency-domain conversion section 254, anextension band estimated spectrum provision section 255, an extensionband gain decoding section 256, a multiplication section 257, atime-domain conversion section 258, and an output terminal 259.

Coding parameters coded by spectrum coding section 210 are input frominput terminal 251, and the coding parameters are sent to extension bandestimated spectrum provision section 255 and extension band gaindecoding section 256 respectively via separation section 252. Also, afirst signal with a 0≦k<FL valid frequency band is input to inputterminal 253. This first signal is the first layer decoded signaldecoded by first layer decoding section 173.

Frequency-domain conversion section 254 performs frequency conversion onthe time-domain signal input from input terminal 253, and calculatesfirst spectrum S1(k). The frequency conversion method used is discreteFourier transform (DFT), discrete cosine transform (DCT), modifieddiscrete cosine transform (MDCT), or the like.

Extension band estimated spectrum provision section 255 generates aspectrum included in extension band FL≦k<FH of first spectrum S1(k) fromfrequency-domain conversion section 254 based on a coding parameterobtained from separation section 252. The generation method depends onthe extension band spectrum estimation method used on the coding side,and it is assumed here that estimated spectrum E(k) included in theextension band is generated using first spectrum S1(k). Therefore,combined spectrum F(k) output from extension band estimated spectrumprovision section 255 is composed of first spectrum S1(k) in band 0≦k<FLand extension band estimated spectrum E(k) in band FL≦k<FH.

Extension band gain decoding section 256 generates subband gaincandidate p(j,n) to be multiplied by the spectrum included in extensionband FL≦k<FH of combined spectrum F(k) based on a coding parameter fromseparation section 252. The method of generating subband gain candidatep(j,n) will be described later herein.

Multiplication section 257 multiplies the spectrum included in FL≦k<FHof combined spectrum F(k) from extension band estimated spectrumprovision section 255 by subband gain candidate p(j,n) from extensionband gain decoding section 256 in subband units, and generates a decodedspectrum F′(k). Decoded spectrum FR) can be expressed as shown inEquation (13).

$\begin{matrix}{{F^{\prime}(k)} = \left\{ \begin{matrix}{F(k)} & \left( {0 \leq k < {FL}} \right) \\{{F(k)} \cdot {p\left( {j,n} \right)}} & \left( {{{FL} + {n \cdot {BWS}}} \leq k < {{FL} + {\left( {n + 1} \right) \cdot {BWS}}}} \right)\end{matrix} \right.} & {{Equation}\mspace{14mu}(13)}\end{matrix}$

Time-domain conversion section 258 converts decoded spectrum F′(k)obtained from multiplication section 257 to a time-domain signal, andoutputs this signal via output terminal 259. Here, processing such assuitable windowing and overlapped addition is performed as necessary toprevent the occurrence of discontinuities between frames.

FIG. 25 is a block diagram showing the main internal configurationelements of above-described extension band gain decoding section 256.

Index j determined by extension band gain coding section 206 on thecoding side is input from an input terminal 261, and gain G(j) isselected and output from a gain codebook 262 based on this indexinformation. This gain G(j) is sent to an interpolation section 263, andinterpolation section 263 performs interpolation in accordance with theabove-described method and generates subband gain candidate p(j,n), andoutputs this from an output terminal 264.

According to this configuration, determined gain can be decoded whilesmoothly approximating variations in the spectrum outline, enabling theoccurrence of degraded sounds to be suppressed and quality to beimproved.

Thus, according to a decoding apparatus of this embodiment, aconfiguration is provided that corresponds to the coding methodaccording to this embodiment, enabling a sound signal to be codedefficiently with a small number of bits, and a good sound signal to beoutput.

Embodiment 3

FIG. 26 is a block diagram showing the main internal configurationelements of an extension band gain coding section 301 in a codingapparatus according to Embodiment 3 of the present invention. Thisextension band gain coding section 301 has a similar basic configurationto extension band gain coding section 206 shown in Embodiment 2, andtherefore identical configuration elements are assigned the same codes,and descriptions thereof are omitted.

A characteristic of this embodiment is that the order of gainquantization value candidates G(j) included in the gain codebook is1—that is, they are scalar values—and gain interpolation is performedbetween a base gain found based on a base amplitude value provided froman input terminal and a gain quantization value candidate G(j).According to this configuration, since the number of gain values subjectto quantization is reduced to 1, lowering of the bit rate is possible.

A base amplitude value input from an input terminal 302, and thelowest-frequency subband amplitude value among subband amplitude valuescalculated by subband amplitude calculation section 212, are sent to abase gain calculation section 303. The base amplitude value here isassumed to be calculated from the spectrum included in a band adjacentto the extension band, as shown in FIG. 27. Base gain calculationsection 303 determines a base gain so as to satisfy the premise that thebase amplitude value and the lowest-frequency subband amplitude valuecoincide. If the base amplitude value is represented by Ab, and thelowest-frequency subband amplitude value by AE(0), base gain gb isexpressed as shown in Equation (14).gb=Ab/AE(0)  Equation (14)

Using base gain gb found by base gain calculation section 303 and gainquantization value candidate g(j) obtained from gain codebook 215, aninterpolation section 304 generates the gain of subbands whose gain isundefined by means of interpolation, as shown in FIG. 28. In thisfigure, number of subbands N=8, and the subbands for which gain isgenerated by interpolation are the 1st through 6th subbands.

Next, the configuration of a decoding apparatus that decodes a signalcoded by a coding apparatus according to this embodiment will bedescribed using FIG. 29. This extension band gain decoding section 350has a similar basic configuration to extension band gain decodingsection 256 shown in Embodiment 2 (see FIG. 25), and therefore identicalconfiguration elements are assigned the same codes, and descriptionsthereof are omitted.

Base gain calculation section 353 is supplied with base amplitude valueAb from an input terminal 351, and subband amplitude value AE(0) of thelowest frequency subband in the estimated spectrum of the extension bandfrom an input terminal 352. The base amplitude value here is assumed tobe calculated from the spectrum included in a band adjacent to theextension band, as already explained using FIG. 27. Base gaincalculation section 353 determines a base gain so as to satisfy thepremise that the base amplitude value and the lowest frequency subbandamplitude value coincide, as explained for the extension band gaincoding section.

Thus, according to this embodiment, the number of gain values subject toquantization is reduced to 1, and further lowering of the bit rate ismade possible.

Embodiment 4

FIG. 30 is a block diagram showing the main configuration elements of anextension band gain coding section 401 in a coding apparatus accordingto Embodiment 4 of the present invention. This extension band gaincoding section 401 has a similar basic configuration to extension bandgain coding section 206 shown in Embodiment 2, and therefore identicalconfiguration elements are assigned the same codes, and descriptionsthereof are omitted.

A characteristic of this embodiment is that a subband with an extremecharacteristic (such as the highest or lowest gain value, for example)among subbands included in the extension band is always included in thegain codebook search objects. According to this configuration, a subbandthat is most subject to the influence of gain can be included in thegain codebook search objects, thereby enabling quality to be improved.However, with this configuration, it is necessary to code additionalinformation as to which subband has been selected.

Using subband amplitude value AE(n) of estimated spectrum E(k) found bysubband amplitude calculation section 212 and subband amplitude valueAS2(n) of second spectrum S2(k) found by subband amplitude calculationsection 218, a subband selection section 402 calculates ideal gain valuegopt(n) in accordance with Equation (15).gopt(n)=AS2(n)/AE(n)  Equation (15)

Next, the subband for which ideal gain value gopt(n) is a maximum (orminimum) is found, and that subband information is output from an outputterminal.

Based on gain candidates G(j)={g0(j), g1(j), g2(j)} and subbandinformation obtained from subband selection section 402, aninterpolation section 403 allocates gain candidates as shown in FIG. 31,and uses interpolation to determine gain for subbands for which gain hasnot been determined. In this figure, gain candidates are allocated tothe 0'th subband and 7th subband by default, and among the 1st through6th subbands, a gain candidate is allocated to the subband that has themost characteristic gain (in this figure, the 2nd subband), and the gainvalues of the other subbands are determined by interpolation.

Next, an extension band gain decoding section 450 in a decodingapparatus that decodes a signal coded by a coding apparatus according tothis embodiment will be described using FIG. 32. This extension bandgain decoding section 450 has a similar basic configuration to extensionband gain decoding section 256 shown in Embodiment 2, and thereforeidentical configuration elements are assigned the same codes, anddescriptions thereof are omitted.

Interpolation section 263 allocates g0(j) to the 0'th subband and g2(j)to the 7th subband based on gain G(j)={g0(j), g1(j), g2(j)} obtainedfrom gain codebook 262 and subband information input via an inputterminal 451, allocates g1(j) to a subband indicated by subbandinformation, and determines the gain of other subbands by means ofinterpolation. Subband gain decoded in this way is output from outputterminal 264.

Thus, according to this embodiment, a subband that is most subject tothe influence of gain is included in the gain codebook search objectsand coded, enabling coding performance to be further improved.

This concludes a description of the embodiments of the presentinvention.

A spectrum coding apparatus according to the present invention is notlimited to above-described Embodiments 1 through 4, and variousvariations and modifications may be possible without departing from thescope of the present invention.

It is also possible for a coding apparatus and decoding apparatusaccording to the present invention to be provided in a communicationterminal apparatus and base station apparatus in a mobile communicationsystem, whereby a communication terminal apparatus and base stationapparatus that have the same kind of operational effects as describedabove can be provided.

Cases have here been described by way of example in which the presentinvention is configured as hardware, but it is also possible for thepresent invention to be implemented by software. For example, the samekind of functions as those of a coding apparatus and decoding apparatusaccording to the present invention can be realized by writing algorithmsof a coding method and decoding method according to the presentinvention in a programming language, storing this program in memory, andhaving it executed by an information processing section.

The function blocks used in the descriptions of the above embodimentsare typically implemented as LSIs, which are integrated circuits. Thesemay be implemented individually as single chips, or a single chip mayincorporate some or all of them.

Here, the term LSI has been used, but the terms IC, system LSI, superLSI, ultra LSI, and so forth may also be used according to differencesin the degree of integration.

The method of implementing integrated circuitry is not limited to LSI,and implementation by means of dedicated circuitry or a general-purposeprocessor may also be used. An FPGA (Field Programmable Gate Array) forwhich programming is possible after LSI fabrication, or a reconfigurableprocessor allowing reconfiguration of circuit cell connections andsettings within an LSI, may also be used.

In the event of the introduction of an integrated circuit implementationtechnology whereby LSI is replaced by a different technology as anadvance in, or derivation from, semiconductor technology, integration ofthe function blocks may of course be performed using that technology.The adaptation of biotechnology or the like is also a possibility.

The present application is based on Japanese Patent Application No.2004-148901 filed on May 19, 2004, entire content of which is expresslyincorporated herein by reference.

INDUSTRIAL APPLICABILITY

A coding apparatus, decoding apparatus, and method thereof according tothe present invention are suitable for use in a communication terminalapparatus or the like in a mobile communication system.

The invention claimed is:
 1. A coding apparatus comprising: anacquisition section that acquires a spectrum of a voice signal includinga low frequency band spectrum and a high frequency band spectrum; afirst coding section that codes the low frequency band spectrum, togenerate first coded information; a first decoding section that decodesthe first coded information, to generate decoded low frequency bandspectrum; a generation section that generates a shape of an estimatedhigh frequency band spectrum by duplicating the decoded low frequencyband spectrum; a first subband amplitude calculation section thatdivides the estimated high frequency band spectrum into a plurality ofsubbands and calculates a first average amplitude value of the estimatedhigh frequency band spectrum in each of the plurality of subbands; asecond subband amplitude calculation section that divides the highfrequency band spectrum into a plurality of subbands and calculates asecond average amplitude value of the high frequency band spectrum ineach of the plurality of subbands; a gain codebook that outputs only again of specific subbands, the specific subbands including a subband ofthe estimated high frequency band spectrum adjacent to the low frequencyband spectrum among the plurality of subbands of the estimated highfrequency band spectrum; an interpolation section that finds a gain of asubband of the estimated high frequency band spectrum other than thespecific subbands by interpolating the gain of the specific subbands; amultiplication section that multiplies the first average amplitude valueby the gain output from the gain codebook or the interpolation sectionin each of the subbands; a second coding section that calculates adistortion between a multiplied result of the multiplication section andthe second average amplitude value and codes only the gain of thespecific subbands when the distortion is smallest; and an outputterminal that outputs coded information obtained by the first and secondcoding sections.
 2. The coding apparatus according to claim 1, whereinthe specific subbands include a subband having a highest frequency bandof the estimated high frequency hand spectrum.
 3. The coding apparatusaccording to claim 1, wherein the specific subbands include a subbandhaving a minimum point of the estimated high frequency band spectrum ora subband having a maximum point of the estimated high frequency bandspectrum.
 4. A layered coding apparatus that generates coded informationhaving scalability in a frequency axis direction, and uses the codingapparatus according to claim 1 for extension layer coding.
 5. A decodingapparatus that decodes coded information relating to a spectrum of avoice signal including a low frequency band spectrum and a highfrequency band spectrum, comprising: a first decoding section thatdecodes coded information relating to the low frequency band spectrum,to generate a decoded low frequency band spectrum; a second decodingsection that decodes coded information relating to the high frequencyband spectrum, to generate only a gain of specific subbands, thespecific subbands including a subband of the high frequency bandspectrum adjacent to the low frequency band spectrum among the pluralityof subbands into which the high frequency band spectrum is divided; anoutput terminal that outputs the decoded low frequency band spectrumobtained by the first decoding section and the gains obtained by thesecond decoding section; an interpolation section that finds a gain of asubband other than the specific subbands by interpolating the gain ofthe specific subbands; and a high frequency band spectrum generationsection that generates the high frequency band spectrum using thedecoded low frequency band spectrum obtained by the first decodingsection and the gains obtained by the second decoding section and theinterpolation section.
 6. A communication terminal apparatus comprisingthe coding apparatus according to claim
 1. 7. A communication terminalapparatus comprising the decoding apparatus according to claim
 5. 8. Abase station apparatus comprising the coding apparatus according toclaim
 1. 9. A base station apparatus comprising the decoding apparatusaccording to claim
 5. 10. A coding method comprising: an acquisitionstep of acquiring a spectrum of a voice signal including a low frequencyband spectrum and a high frequency band spectrum; a first coding step ofcoding the low frequency band spectrum, to generate first codedinformation; a first decoding step of decoding the first codedinformation, to generate decoded low frequency hand spectrum; ageneration step of generating a shape of an estimated high frequencyband spectrum by duplicating the decoded low frequency band spectrum; afirst subband amplitude calculation step of dividing the estimated highfrequency band spectrum into a plurality of subbands and calculating afirst average amplitude value of the estimated high frequency bandspectrum in each of the plurality of subbands; a second subbandamplitude calculation step of dividing the high frequency band spectruminto a plurality of subbands and calculating a second average amplitudevalue of the high frequency band spectrum in each of the plurality ofsubbands; a gain output step of outputting only a gain of specificsubbands, the specific subbands including a subband of the estimatedhigh frequency band spectrum adjacent to the low frequency band spectrumamong the plurality of subbands of the estimated high frequency handspectrum; an interpolation step of finding a gain of a subband of theestimated high frequency band spectrum other than the specific subbandsby interpolating the gain of the specific subbands; a multiplicationstep of multiplying the first average amplitude value by the gain outputfrom the gain output step or the interpolation step in each of thesubbands; a second coding step of calculating a distortion between amultiplied result of the multiplication step and the second averageamplitude value and coding only the gain of the specific subbands whenthe distortion is smallest; and an output step of outputting codedinformation obtained by the first and second coding steps.
 11. Adecoding method that decodes coded information relating to a spectrum ofa voice signal including a low frequency band spectrum and a highfrequency band spectrum, comprising: a first decoding step of decodingcoded information relating to the low frequency band spectrum, togenerate a decoded low frequency band spectrum; a second decoding stepof decoding coded information relating to the high frequency bandspectrum, to generate only a gain of specific subbands, the specificsubbands including a subband of the high frequency band spectrumadjacent to the low frequency band spectrum among the plurality ofsubbands into which the high frequency band spectrum is divided; aninterpolation step of finding a gain of a subband other than thespecific subbands by interpolating the gain of the specific subbands;and a high frequency band spectrum generation step of generating thehigh frequency band spectrum using the decoded low frequency bandspectrum obtained by the first decoding step and the gains obtained bythe second decoding step and the interpolation step.